Papers by Keyword: Carbon Clusters

Abstract: Methyl, methoxy and alcoxy groups with different number of carbon atoms were chemically grafted onto the surface of fumed silica nanoparticles. After chemical modification the nanopowders were annealed in vacuum at 700 °C. The effect of the amount of carbon atoms in grafted hydrocarbon groups and type of bonding to silica surface (Si-C v.s. Si-O-C) were studied. It was demonstrated that carbon incorporation results in the development of broad band photoluminescence that covers the wholevisible spectral range. Increasing of carbon incorporation resulted in increasing of photoluminescence intensity and red shift of the photoluminescence band maximum.

Abstract: Structures to Be Based on Hafnium Dioxide Are Regarded as the Most Perspective High-K Dielectric for Integration in MOS-Technology, Carbon Nanotubes Transistors. MOCVD (Metal-Organic Chemical Vapor Deposition) Techniques of HfO₂, Al₂O₃ and (Al₂O₃)_x(HfO₂)1-X Thin Films Were Applied Using Metal-Organic Substances as the Precursors. Dependences of Growth Rates on Process Parameters Were Studied. The Chemical Structure and Properties of the Films and Electrophysical Characteristics of the Test Structures Were Investigated.

Abstract: High-resolution transmission electron microscopy (HR TEM) reveals an atomically flat SiC surface after oxidation in either NO or dry O2 ambients. This reopens the question of the origin of the electronically active defects at the SiO2–SiC interface, whose density remains orders of magnitude higher than in the SiO2–Si interface. Capacitance-transient measurements, analysed in this paper, demonstrate that the dominant electronically active defects are in the oxide at tunneling distances from the SiC surface (near-interface traps). The HR TEM results cannot rule out that these traps are related to carbon/oxygen bonds or even nanometer-sized carbon clusters, which resolves the apparent inconsistency with the earlier experimental evidence of carbon accumulation at (or near) the SiO2–SiC interface.

Abstract: We observe new photoluminescence centers in electron-irradiated 6H-SiC with phonon replicas up to 250 meV and clear threefold isotope splitting of the highest energy mode. Based on ab initio calculations, we discuss the tri-carbon anti-site (C3)Si and the di-interstitial (C2)Hex as models for these centers.

Abstract: A growing number of recent publications on clusters reflect a tremendous interest in these particles. These studies reveal new fundamental physical and chemical aspects of matter. Clusters are called the fifth state of matter: liquid, solid, cluster, gas and plasma. In this work, a carbon cluster was generated by a spark cluster source and detected by single focusing mass spectrometer in situ. We examined the effects of cluster source parameters on the generation of carbon cluster and report our initial results. This method should be useful for studying the mechanism of fullerene formation. In the case when carbon clusters generated in plasma arc are carried by the Ar or H2 gas flow downstream through a vacuum chamber to the ion source of mass spectrometer, we obtained a small binary carbon cluster C28H4 (hydrogenated fullerene). The empty fullerene is tetravalent and strongly binds four hydrogen atoms, which significantly weakens two different sets of bonds and leads to an open-shell electronic structure. Conclusion is that endohedral C28H4 are hypervalent. We have demonstrated how in situ mass spectrometry has led to the rapid development of an important branch of synthetic fullerene chemistry that has yielded many new small fullerenes and related derivatives with novel structures and properties. The impact of mass spectrometry on the synthesis of fullerene derivatives is the subject of this paper. Significantly, a large fraction of products could be condensed on a specially designed collection plate, which allows further spectroscopic characterization of new derivatives.

Abstract: The mechanisms of oxygen incorporation during dry thermal oxidation of 6H-SiC wafers were investigated. Isotopic tracing of oxygen was performed by sequential oxidations in dry O2 enriched or not in the 18O isotope and subsequent determinations of the 18O profiles. The results obtained with SiC substrates were compared with those of Si, evidencing different mechanisms of oxygen incorporation and transport. The gradual nature of the SiO2/SiC interface was also evidenced. A probable explanation for this gradual SiO2/SiC interface is shown to be the formation of C clusters during oxidation.

Abstract: In this work, we present results on the study of bonding and concentration of carbon in 4H-SiC MOS structure by x-ray photoelectron spectroscopy (XPS). The XPS spectra were fitted by several Gaussian lineshape functions. It is found that the so-called carbon clusters (C-C bonds) appear at the interface of SiO2/SiC, but are not seen in the oxide bulk. However, there are still some SiOxCy and Si-C bonds inside the oxide and the integrated area ratio of SiOxCy/Si-C bonds increases when further away from the SiO2/SiC interface. These observations can be interpreted in terms of the dynamic oxidation process that transforms Si-C bonds into SiOxCy bonds, which are then further oxidized to form SiO2 bonds.

Abstract: Properties of defects encountered at the oxidized surfaces of silicon carbide (SiC) suggest their origin to be different from the dangling-bond-type defects commonly observed in the oxidized silicon. Among different models of these SiC/oxide interface states advanced during the past decade, two have received substantial experimental support. This first one is the “carbon cluster” model, which ascribes the traps with energy levels in the SiC bandgap to inclusions of elemental carbon formed during the SiC surface treatment and subsequent oxidation. The second model invokes intrinsic defects of SiO2 to account for the high density of interface states in the energy range close to the conduction band of SiC. Achievements in reducing the SiC/SiO2 defect density are discussed.